Inferring the phylogenetic relationships within two fish genera: insights into the biogeography of the northern Gulf of Mexico
Hunt, Elizabeth P.
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A suture zone can be defined as a geographic area where faunal assemblages meet and in which pairs of taxa (species, semi-species, etc.) have come back into secondary contact and may hybridize. While identifying these areas in terrestrial and freshwater environments has been an active area of research, less work has taken place in marine systems, in part, because barriers to dispersal are less apparent. In the northern Gulf of Mexico at least 15 putative sister taxa meet, with some evidence of hybridization, in an area roughly centered south of Mobile Bay (~88°W). This is consistent with the presence of a northern Gulf suture-zone, but data verifying the relationships between putative sister species are lacking. Therefore, in this study, phylogenetic relationships between species in the genera Ogcocephalus and Sphoeroides, were assessed using massively parallel sequencing of genomic libraries enriched for ultra-conserved DNA elements, with a focus on putative sister species distributed on either side of the hypothesized suture zone. Results of maximum likelihood and species tree analyses reveal multiple instances of speciation resulting in an eastern Pacific and western Atlantic species of Sphoeroides, as opposed to a single diversification event in either region. Further, S. nephelus (western Gulf) and S. parvus (eastern Gulf) were not resolved in a sister relationship, but instead formed a monophyletic group with S. maculatus (Atlantic) and the relationships between the three species and their distributions mirrors that of other taxa in this region. Ogcocephalus parvus (eastern Gulf and Atlantic) and O. declivirostris (western Gulf) were not resolved as sister taxa as previously described. Instead, O. declivirostris was consistently resolved in a group with O. corniger (eastern Gulf), although each species is not monophyletic. Relationships between O. pantostictus, O. cubifrons, and O. radiatus are also left unresolved as these three putative species also did not form exclusive lineages. The discordance seen between species and phylogenetic placement in this genus could be a result of several different factors including erroneous classification, misidentifications, and/or insufficient lineage sorting between taxa, and further study is warranted.
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